(a) Technical Field
The present disclosure relates generally to a method for determining an amount of regenerative braking. More particularly, it relates to a method for determining an amount of regenerative braking to maximize the amount of regenerative braking by making an early stage control of the regenerative braking be performed at an early stage of braking.
(b) Background Art
The travelling modes of hybrid vehicles include an Electric Vehicle (EV) mode which is a pure electric vehicle mode using only a motor power, a Hybrid Electric Vehicle (HEV) mode which utilizes an engine as the primary power source and a motor as auxiliary power, and a Regenerative Braking (RB) mode which charges a battery by recovering brake and inertial energy of the vehicle while travelling due to braking or inertia of the vehicle.
With respect to the latter, regenerative braking is a technology which generates electric energy using a motor, stores generated electric energy using a high voltage battery, and reuses the electric energy at the time of driving the vehicle by applying an inverse torque to the electric motor using energy generated during braking in order to maximize the vehicle's fuel ratio. Regenerative braking technology has been applied to most environment friendly vehicles, such as hybrid cars, electric cars, fuel cell cars, and the like. In the case of hybrid cars, regenerative braking plays a large role in fuel ratio improvement to such an extent that the regenerative braking is the primary driver for fuel ratio improvement in comparison to a general vehicle.
Regenerative braking is typically performed through a coordinated control of an electric brake device (i.e., EBS: Electric Brake System) which takes charge of a hydraulic brake and a hybrid controller (i.e., HCU: Hybrid Control Unit) which is an upper level controller of the hybrid vehicle. In this regard, FIGS. 1 and 2 illustrate a conventional regenerative braking procedure performed through a coordinated control between the EBS and the HCU. As shown in FIGS. 1 and 2, the procedure of the coordinated control between the EBS and the HCU consists of steps of inputting a required amount of braking into the EBS as a driver presses a brake pedal, determining a permissible amount of regenerative braking by the EBS, determining an amount of execution of regenerative braking according to the permissible amount of regenerative braking by the HCU, determining an amount of friction braking by the EBS according to the amount of execution of regenerative braking determined by the HCU and performing a friction braking control, and performing a regenerative braking control by a motor controller (i.e., MCU: Motor Control Unit) according to the amount of execution of regenerative braking determined by the HCU.
However, since vehicle braking is in close relation to safety, the hydraulic braking (i.e., friction braking device) is deemed to have a priority over the regenerative braking in the above mentioned coordinated control. Furthermore a case may occur where the regenerative braking is limited due to reasons of motor temperature, a battery charge condition, a speed change procedure of a transmission, and the like.
Meanwhile, at the time of braking, in case of performing the hydraulic braking after first checking whether the regenerative braking is actuated without performing the hydraulic braking, since a brake delay time of at least 20 ms can be generated, there may be a risk of accidents. Therefore, since at the early stage of braking, the hydraulic braking of at least 1 bar is first performed, and thereafter the hydraulic control is performed by judging the necessity of the regenerative braking, there is a loss of the amount of regenerative braking as much as an amount of oil pressure. That is, a problem as follows may occur:
First, there is a problem of fuel ratio aggravation. The regenerative braking is a technology of converting energy into electric energy at the time of braking and is directly related to the fuel ratio, so that an increase in the amount of regenerative braking at once equates to fuel ratio improvement. However, since the hydraulic braking is first performed to secure the braking safety, i.e., since the hydraulic pressure is unconditionally first used at the time of early stage braking, fuel ratio aggravation due to the loss of the amount of regenerative braking is caused.
Second, there is a problem of aggravation of drive. At the early stage of braking, a control is performed in such a way that an oil pressure of at least 1 bar is applied. Thereafter, a total amount of braking of the regenerative braking and the hydraulic braking is made according to the amount of braking that a driver requires by reducing the oil pressure at the time of performing the regenerative braking. However, since the response of the regenerative braking is slow, there may occur a feeling of suddenness and discomfort at the initial stage of braking, and in the case of downward adjusting the increase gradient of the amount of regenerative braking to minimize the discomfort, eventually, a vicious circle of reducing the amount of regenerative braking and aggravating the fuel ratio is repeated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the related art that is already known in this country to a person of ordinary skill in the art.